1. Field of the Invention
The present invention relates to a power supply unit and an electronic apparatus using the power supply unit. More particularly, the present invention relates to a power supply unit using a momentary type power switch and an electronic apparatus using the power supply unit. More particularly, the present invention pertains to a power supply unit realizing a remote power on/off scheme using the momentary switch and an electronic apparatus unit using the power supply unit.
2. Related Art
Due to a recent technical revolution, various small size and light weight electrical and electronic apparatuses with an excellent mobility, a notebook personal computer (PC) for example, have been developed. Among them, the notebook PC is designed and fabricated to be small size and light weight with taking consideration of a mobile environment, i.e. use in outdoor requiring portability and mobility. One example of the notebook PC is xe2x80x9cIBM ThinkPad 760xe2x80x9d series marketed by IBM Japan, Ltd (The xe2x80x9cThinkPadxe2x80x9d is a trademark of International Business Machines Corporation). The ThinkPad 760 is a clam shell structure which contains a thin main body and a cover member pivotally mounted to about rear edge of the main body, as shown in the FIG. 5. A system board on which a CPU, a memory and various controller chips are mounted is contained within the main body. Also, a hard disk drive (HDD), a floppy disk drive (FDD), and a CD-ROM drive etc., as external storage device, are accommodated into the main body. Also, a key board unit as an input device is mounted on an upper surface of the main body. A liquid crystal display (LCD) unit is embedded within the cover member. An operator can perform a key input with seeing the LCD unit by opening the clam shell cover member. Also, by closing the clam shell cover member, the key board unit and the LCD unit are protectively placed within the personal computer for carrying it. Generally, the notebook PC is a battery powered type which is driven by the battery, since the PC is designed to use it in the mobile environment where a commercial power supply is not available.
Recently, a remote on/off scheme using a momentary type (return type) switch has been frequently used as the power supply on /off circuit scheme of these electronic apparatuses. For example, the above described notebook PC xe2x80x9cThinkPadxe2x80x9d series uses the momentary switch as the power switch, to enable the control of the power on/off by a single hand.
The FIG. 6 shows a block diagram of major parts of the on/off mechanism of a conventional power supply system using the momentary switch. As shown in the FIG. 6, a main power source of the electronic apparatus is a battery 20, and the battery 20 is detachably and exchangeably connected through a connector. An output current of the battery 20 is supplied to a DC/DC converter 50 through a main power line 10. The DC/DC converter 50 converts the DC voltage of the battery 20 to a level suitable for a system operation, and supplies it to various portions of a system load. A switch SW2 is inserted on the way of the main power line 10 to turn on/off the output of the main power source. An example of the switch SW2 is a P channel type FET switch.
A power switch (SW1) by which an user can indicate the power on/off of the apparatus is mounted on a surface of an outer wall of a housing of the electronic apparatus. If this power switch SW1 is the momentary switch, the switch SW1 returns to the original position when the user manipulation is terminated. Because the switch SW1 stays at the same position, the switch SW1 itself can not store the current manipulated state, i.e. the power on state or the power off state. To one end of the switch SW1, a latch circuit 30 is connected which stores the current manipulated state of the momentary switch SWI, and the on/off control of the switch SW2 is performed by the output of the latch circuit 30 rather than the direct output of the momentary switch SW1. To be brief, the power on/off operation of the electronic apparatus is remotely made by the latch circuit rather than made directly by the momentary switch SW1.
The latch circuit 30 requires a drive voltage. In the example shown in the FIG. 6, the latch circuit 30 is applied with a drive voltage VCC from the main power line 10. Even when the electronic apparatus is powered off, the drive voltage VCC is required to store the manipulated state of the momentary switch SW1. Therefore, the drive voltage VCC must be supplied from a node located at the upper stream, i.e. a source side, of the switch SW2, which is always powered even when the switch SW2 is turned off, rather than a node located at the down stream, i.e. a drain side, of the switch SW2, which is powered off when the SW2 is turned off. However, it means that a leak current continuously flows through the latch circuit 30 even when the apparatus is powered off, and that the supply of the drive voltage VCC causes an undesired power consumption. In the case that the electronic apparatus is a battery powered type, the leak current flowing from the battery during a long power off period of the electronic apparatus can not be ignored.
Particularly, a requirement has been recently increased to ship the electronic apparatus from a factory with the battery being accommodated into a battery room within the PC body. It is because a user wants to operate the PC at the time he or she opens the package to display system set up instructions on the display unit (it is called as xe2x80x9cInstant Onxe2x80x9d) so that the usability is increased, and because a space in the package for packaging the battery becomes unnecessary thereby saving the costs. However, in the case that a delivery period from the factory to users exceeds several months, the over discharge of the battery may arise due to the leak current to the latch circuit as above described. The over discharge may causes the degradation of the characteristic of the battery, resulting in the increase of the claims by the users.
The object of the present invention is to provide an excellent electronic apparatus and a power supply unit used into the electronic apparatus which eliminate a leak current during a power off period.
The further object of the present invention is to provide an excellent electronic apparatus and a power supply unit used into the electronic apparatus which use a momentary type power switch.
The further object of the present invention is to provide an electronic apparatus and a power supply unit used into the electronic apparatus which realize a remote power on/off scheme using the momentary switch without a leak of current at a power off period.
The operation of the present invention is described with reference to the FIG. 1. The FIG. 1 schematically shows the power supply unit operated in the remote power on/off scheme which embodies the present invention.
The electronic apparatus containing the power supply unit uses a battery 20 as a main power source, and the battery 20 is detachably and exchangeably connected at a connector portion. An output current of the battery 20 is supplied to a DC/DC converter 50 through a main power line 10. It is substantially the same as that of the prior circuit shown in the FIG. 6 that the DC voltage from the battery 20 is converted to a voltage level by the DC/DC converter 50 and the voltage level is applied to the various portions of a system load 100, and that a switch (SW2) for turning on/off the output of the main power supply is connected on the way of the main power line 10. The switch SW2 may be a P channel type FET, for example.
A momentary switch (SW1) by which an user controls the power on/off of the electronic apparatus is mounted on a surface of an outer wall of the electronic apparatus. One terminal of the momentary switch SW1 is inputted to the latch circuit 30 and a switch drive circuit 40, and the other terminal of the momentary switch SW1 is connected to a ground potential. The latch circuit 30 is provided to store the current manipulated state of the momentary switch SW1. Since a drive voltage VCC of the latch circuit 30 is applied from a node located at the down stream, i.e. a drain side, of the switch SW2, the power to the latch circuit 30 is not supplied when the switch SW2 is turned off, and hence the latch circuit 30 can not latch the manipulated state of the momentary switch SW1. The switch drive circuit 40 turns the switch SW2 on in response to the operation of the momentary switch SW1 in the turn off state of the switch SW2. More particularly, when the P channel FET switch SW2 is in the turn off state, the switch drive circuit 40 connects a gate terminal of the P channel FET switch SW2 to the ground potential in response to the operation of the momentary switch SW1. The switch drive circuit 40 does not consume power in the turn off state of the switch SW2 (i.e. the turn off state of the power supply unit), and can turn the switch SW2 on in the non-powered state (i.e. the state in which the drive voltage is not supplied), in the manner as described.
The power on operation in the power supply system proceeds as below. In the power off state i.e. the state in which switch SW2 is turned off, the power is not consumed since the power is not supplied to the latch circuit 30. Also, at this point of time, the switch drive circuit 40 does not consume the power. When the user depresses the switch SW1 during the turn off state of the switch SW2, the switch drive circuit 40 turns the switch SW2 on. As a result, the latch circuit 30 becomes possible to receive the drive voltage VCC from the node located at the down stream of the switch SW2, becomes possible to latch the turn on state of the momentary switch SW1. After this, when the user releases the momentary switch SW1, the momentary switch SW1 itself immediately returns to its original position, so that the turn on operation of the switch SW2 by the switch drive circuit 40 is terminated. However, at this point of time, it becomes possible to maintain the turn on state of the switch SW2 by the operation of the latch circuit 30.
When the system is in the power off state, i.e. the state in which the switch SW2 is turned off, the power is not supplied to the latch circuit 30. Also, since the switch drive circuit 40 does not require any drive voltage to turn the switch SW2 on, the power loss does not arise even if the system is not used during a long period. Accordingly, even if the electronic apparatus with the battery is not used during a long period, the power loss of the battery due to the leak current does not arise.
In summary, in accordance with the present invention, it is possible to provide an excellent electronic apparatus and a power supply unit used in the electronic apparatus which eliminate a leak current during a power off period.
Also, in accordance with the present invention, it is possible to provide an excellent electronic apparatus and a power supply unit used in the electronic apparatus which use a momentary type power switch.
Also, in accordance with the present invention, it is possible to provide an electronic apparatus and a power supply unit used in the electronic apparatus which realize a remote power on/off scheme using the momentary switch without a leak of current during a power off.
Further objects, characteristics and advantages of the present invention will be apparent from the detail description based upon the embodiments of the present invention and the drawings.